Research Division Seminar
(Re)solving Reionization with Lyman-alpha emission

Abstract

The Epoch of Reionization (EoR) was the last major phase transition of the Universe. While the timeline of reionization is increasingly well-constrained, its sources remain elusive. Due to their number density, star-forming galaxies are the likeliest candidates, but whether the ionizing photon budget arose from a multitude of ultra-faint galaxies or a rarer set of bright galaxies is a key open question. The key uncertainty is the ionizing photon escape fraction (LyC Fesc), and how this varies among galaxy properties. In my talk I will argue to tackle this problem based on measurements of resolved Lyman-alpha (LyA) emission from the X-SHOOTER LyA survey at z=2 (XLS-z2). I will show observational evidence that the defining traits of LyC leaking galaxies are highly ionising stellar populations, low column density gas and a dust-free, high ionization state ISM. This is evidence that galaxies leak ionising photons (with LyC Fesc 20-50 %) when the hottest stars are still shining. Motivated by these results, I will present a model of a LyA Emitter-dominated emissivity that explains the relative flatness of the total galaxy emissivity over z~2-8 and the reionization of the Universe by z~6 under reasonable assumptions, thus naturally accounting for the strong evolution of the average LyC Fesc of the full galaxy population between redshifts z~2-8. In a fiducial choice of model parameters, the "disco" emissivity is dominated by a strong minority of galaxies with intermediate mass (~10^{^8} Msun). I will conclude with proposed observational tests to further develop the LyA-anchored formalism. 

Zoom link: 
https://rediris.zoom.us/j/85785567444?pwd=ckNnYzMyQk9WRHI0MFRROWJ1QnJWdz09
Meeting ID: 857 8556 7444

Passcode: 058978

YouTube: https://youtu.be/iNmNi-bTKtM